Toroids and electronic radiation - diyAudio
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Old 15th July 2003, 02:01 PM   #1
Elkaid is offline Elkaid  Canada
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Default Toroids and electronic radiation

Do toroids have tendencies to induce noise in components when placed too close ?.

By example, if I place an Op-Amp or a signal wire too close of a toroid transformer, will it induce noise or other indersirable things ? What are safe distances ?

I know that standard "rectangle" transformer radiate a bit (I suppose that's why aligment is so important in tube amplifier) but is it the same thing with Toroids ? R core ?

Thanks for your help !

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Old 15th July 2003, 03:33 PM   #2
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Toroids DO induce noise in components when placed closed to them, however the induction is much smaller than for the "old" standard "rectangle" transformers.
Personally I only place non-active components near a toroid. If I have to place an active component (like an Op-Amp or a transistor) I always use a shielding metal plate to awoid induction, and never place signal wires close to the toroid.
I don't think you can "calculate" the safe distance, because this depends on many factors like the way the toroid are wounded, the internal layout of the active components, pin length etc.
You can infact hear the induction noice, by moving a signal wire over and along the sides of the toroid.
Does somebody have other experiences????
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Old 15th July 2003, 04:35 PM   #3
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You Bet! I had to place a copper shield around my toroid because it induced hum into my signal wires that run beside it. Got some flashing from the local hardware store and cut a band to go around the outside. See photo
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Old 15th July 2003, 05:26 PM   #4
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Hi Elkaid,
Seems very much the same as my solutions

What are your experiences with main wires around the chassis..?
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Old 15th July 2003, 05:30 PM   #5
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Default not Cu, Fe

if you want to shield the transformer iron (muMetal) will do the trick

I believe that pot-core transformers have the lowest radiation.
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Old 15th July 2003, 05:36 PM   #6
Elkaid is offline Elkaid  Canada
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is Fe better than Cu ?

A few month ago, we were using sheets of Cu to shield PowerLine transmitters prototypes from RF noise. It seems to work fine but that couldn't make us win the bakeoff though. (Anyway, that's another story)

So, is Fe better in shielding LF noise than Cu ? Or is it something more "subtile" ?

Thanks !
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Old 15th July 2003, 05:44 PM   #7
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I personally don't think that there are a big difference because Cu also has a low resistance as Fe. I think that the result is determent by the actual way the schielding is made (please also renember that if you use perforated plates for shielding, that the holes are smaller than the wave lenght of the RF-signal that you wich to schield out)....
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Old 15th July 2003, 05:50 PM   #8
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Quote:
if you use perforated plates for shielding, that the holes are smaller than the wave lenght of the RF-signal that you wich to schield out
Uhhhh...
If I'd like to filter out 60Hz noise by example, how can you convert a frequency to a distance (diameter) ?

Also, using a non-perforated plate will block any frequencies ?
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Old 15th July 2003, 05:58 PM   #9
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Quote:
Originally posted by Eric
You Bet! I had to place a copper shield around my toroid because it induced hum into my signal wires that run beside it. Got some flashing from the local hardware store and cut a band to go around the outside. See photo
Did the hum go away?

Maybe you had capacitve coupling? May I ask why you have your cables so loose and near the transformer? Ground rule must be: keep away everything from the transformer. I notice also that your 115/230 volt primary is very close to one of the secondary winding.
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Old 15th July 2003, 06:03 PM   #10
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To calculate the wave-lenght:

Wave lenght in meter = 300000 / the frequency in kHz, so you would need rather big holes to let 60 Hz pass through

Thats why you can have air circulation holes in your cabinet without problems.

In theory, all frequencies should be blocked by a massive plate. But thats theory........
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